The present invention relates to a method for depositing a thin film layer for an element, and an organic electroluminescence element (referred to as an organic EL element), specifically to a method for depositing a thin layer/thin film layers for an element, comprising depositing two or more materials to be deposited (referred to as a material) by vacuum evaporation, so as to form one or more thin layers superior in homogeneity on a substrate to be deposited (referred to as a substrate), and an organic EL element produced by this film-depositing method.
Recently, for display and so on, attention has been paid to organic EL elements and they have been researched. In general, organic EL elements basically have a transparent electrode (anode), a luminous layer made of an organic material, and an opposite electrode (cathode). Many of the organic EL elements further have an electron injection layer, a hole injection layer and so on, in order to improve luminescent property, and have a structure wherein these are deposited into a lamination on a substrate. This is a principle that luminescence is caused by recombination in the luminous layer of an electron injected from the cathode to the luminous layer with a hole injected from the anode to the luminous layer.
For elements having a structure wherein thin film layers are deposited into a lamination, such as organic EL elements as described above, the respective layers are deposited by vacuum evaporation in many cases.
However, if thin film layers are deposited into a lamination on a substrate having a large screen by this vacuum evaporation, a problem that homogeneous films cannot be formed arises. Therefore, many substrate pieces cannot be arranged in a substrate of a large area so that mass production is not allowed. If a large-sized device is produced, luminescence variation is generated in the luminous plane thereof so that the device becomes a defective product.
Against such problems, JP-A-10-335062 suggests a method in which the relationship between the deposition position, on a substrate, of a material, and the vapor density thereof is represented by a function of cosnxcex8, the n value thereof is set to 3 to 6, and an evaporation source thereof is set to a position apart from the center of the substrate. By this method, however, it is difficult to form a homogenous thin film on a substrate having a large screen. Thus, the variation of luminescence performance cannot be overcome just yet. Accordingly, the following points are unsolved problems from the viewpoint that in an organic EL element or the like element which has a structure wherein thin film layers are deposited into a lamination on a substrate having a large screen, the homogeneity of luminescence performance at respective positions in the element is kept.
(1) In the case that thin films are deposited into a lamination, change in the film thickness of each of the films is large at respective positions on a deposition substrate. Thus, in the case of an organic EL element, the variation of luminescence performance is generated inside the plane of the element.
(2) In the case that, for an organic EL element or the like element, a host material and a dopant material of its luminous layer are co-evaporated as evaporation sources, the density of the dopant is not constant in the plane of the element so that the variation of luminescence performance is generated.
The present invention has been made from the above-mentioned viewpoints. An object of the present invention is to provide a method for depositing a homogeneous thin film layer for an element, even on a deposition substrate having a large screen, by vacuum evaporation, the method being capable of attaining the following. In the case of depositing many layers into a lamination, change in the film thickness of each of the films can be made small at respective positions on a deposition substrate. In the case of co-evaporating plural evaporation sources, change in the density of each of the materials can be made small at respective positions on a deposition substrate.
Another object of the present invention is to provide an organic EL element which is produced by such a method for depositing a thin film layer for an element, and which is small in the variation of luminescence performance at respective positions in the element.
In order to attain the above-mentioned objects, the inventors made eager investigations. As a result, the inventors have found out that in the case plural materials are deposited into films by vacuum evaporation, the uniformity of the film thicknesses can be made very high if the relationship between the position of the material i to be deposited on a deposition substrate and the film thickness of the deposited film is represented by cosnixcex8 and the ni value of each of the materials is controlled within a specified range. On the basis of such a finding, the present invention has been made. Therefore, the subject matters of the present invention are as follows.
(1) A method for an element of forming one or more thin films on a substrate by depositing two or more materials by vacuum evaporation, comprising, depositing each material under such control that ni value of the each material is kxc2x10.5 wherein k is a constant from 2 to 5,
when relationship between a deposition position and a film thickness of a material i on the substrate is approximated by the following expression (1):
Di/D0xe2x88x9d(L0/Li)3 cosnixcex8ixe2x80x83xe2x80x83(1) 
wherein L0 is a distance from an evaporation source to a plane of the substrate in a perpendicular direction, D0i is a film thickness of the material i at an intersection point of a perpendicular line from the evaporation source to the plane of the substrate, and Di is a film thickness of the material i at a position on the substrate which is apart from the evaporation source by a distance Li in a direction of an angle xcex8i against the perpendicular line.
(2) The method according to item (1), wherein k is 2 to 3.
(3) The method according to item (1), wherein k is 2.
(4) The method according to any one of items (1) to (3), wherein the ni value is controlled by (a) a method of adjusting a shape of a crucible for holding the evaporation source and/or (b) a method of adjusting evaporation rate.
(5) The method according to any one of items (1) to (4), wherein two or more materials are successively deposited to form a lamination of thin film layers.
(6) The method according to any one of items (1) to (4), wherein two or more materials are simultaneously deposited to form one film.
(7) The method according to any one of items (1) to (6), wherein a material is deposited by an eccentric rotation evaporation method.
(8) The method according to any one of items (1) to (7), wherein the materials are organic materials for organic layers of an organic electroluminescence element and the layers are formed by using the materials.
(9) The method according to item (6), wherein the materials are a host material and a dopant material of a luminous layer of an organic electroluminescence element, and the luminous layer is formed by co-depositing the host and dopant materials.
(10) An organic electroluminescence element comprising organic layers formed by the method according to item (8).
(11) The organic electroluminescence element comprising a luminous layer formed by the method according to item (9).
(12) The organic electroluminescence element according to items (10) or (11), wherein variation of X coordinate of CIE luminescence chromaticity is 0.005/250 mm or less and variation of Y coordinate thereof is 0.02/250 mm or less.
(13) The organic electroluminescence element according to any one of items (10) to (12), wherein variation of electric power conversion efficiency is 15%/250 mm or less.